Machine Type Communication (MTC) is a form of data communication which involves one or more entities that do not necessarily need human interaction. One Study Item was opened in 3GPP Rel10 led by RAN2 discussing the RAN optimization for MTC (cf. document [1]). Before it came to any conclusion, another Work Item pre-empts focusing on the RAN optimization to avoid Core Network overload (cf. document [2]).
Currently, the Rel10 Work Item [2] is almost completed, wherein a “delay tolerant access” has been agreed to identify the delay tolerant request using one of the spare value of RRC establishment cause. When eNB detects the cause, it could set an extended wait timer when responding to the request message so that the UE could be delayed from access reattempt for a longer time period up to 30 minutes.
The Rel10 Study Item [1] resumed from the RAN2#73bis meeting limiting to RAN overload control only. In the RAN2#73bis meeting, it was agreed that Extension of Access Barring (EAB) based on SA1 requirements will be introduced as the baseline for RAN overload control in Rel-11 (cf. document [3]). Therefore, in the present application, it will be discussed how to implement EAB for Rel11.
The SA1 requirements on EAB are described in document [4]. According to this document, “Extended Access Barring (EAB) is a mechanism for the operator(s) to control Mobile Originating access attempts from UEs that are configured for EAB in order to prevent overload of the access network and/or the core network”. More specifically, it requires that EAB information shall define whether EAB applies to UEs within one of the following categories:                a) UEs that are configured for EAB;        b) UEs that are configured for EAB and are neither in their HPLMN nor in a PLMN that is equivalent to it;        c) UEs that are configured for EAB and are neither in the PLMN listed as most preferred PLMN of the country where the UE is roaming in the operator-defined PLMN selector list on the SIM/USIM, nor in their HPLMN nor in a PLMN that is equivalent to their HPLMN        
Therefore, the EAB should differentiate the UEs among the three categories and apply different barring policies/values to them. Moreover, it is observed that category b) is a subset of category a), and that category c) is a subset of category b). UEs within category c) belong to category b) and a) as well. Then, which category the UE should apply when it belongs to multiple category should be defined.
The straightforward way to implement EAB is to apply the same principle as is defined in current specification, i.e. define three set of access class parameters to above categories, respectively. However, this leads to signaling overhead to SIB.
Therefore, according to the present invention, some methods to enable the EAB with less overhead are proposed.
Currently, according to document [5], two sets of access class (AC) barring parameters are defined for the access requests where the establishment cause is set as “mobile originating signaling” and “mobile originating data” access requests, respectively. Within each set, three parameters are defined:                ac-barring factor: If the random number drawn by the UE is lower than this value, access is allowed. Otherwise the access is barred;        Ac-barringtime: Mean access barring time value in seconds;        Ac-barringforspecialAC: Access class barring for AC11-15. The first/leftmost bit is for AC 11, the second bit is for AC 12, and so on.        
In addition to above two sets of ac barring parameters, service specific access barring (SSAC) and ac barring for CSFB (CS Fallback) are also defined.                Ac-barringCSFB: includes a set of access class barring parameters which are applied for mobile originating CS fallback calls;        ssac-BarringForMMTEL-Voice: includes a set of access class barring parameters which are applied for MMTEL voice originating calls;        ssac-BarringForMMTEL-Video: includes a set of access class barring parameters which are applied for MMTEL video originating calls.        
These AC barring mechanisms do not treat UEs that are configured for EAB. Moreover, such set includes configuration for special AC, however, UEs with special AC should be given higher priority and therefore could be excluded from EAB parameters.
In GERAN (GSM EDGE Radio Access Network), some companies proposed to define extended access classes to enable EAB (cf. document [6]). However, the newly defined access classes are required. However, it was not agreed by CT1 and EAB is expected to be defined without new access classes.
The following documents are referred to in the present application:    [1] RP-100330, RAN Improvements for Machine-type Communications;    [2] RP-101026, RAN mechanisms to avoid CN overload due to Machine-Type Communications;    [3] R2-112661 Draft report of RAN2 #73bis, Shanghai, China;    [4] 3GPP TS 22.011 V10.3.0;    [5] 3GPP TS 36.331 v10.1.0;    [6] GP-101903, realizing extended access barring, Telefon AB LM Ericsson, ST-Ericsson.